One challenge that writing instrument designers have historically faced is to prevent or to inhibit undesired leakage of ink from the writing instrument, while maintaining ease of writing, uniformity of performance, and other beneficial properties of the ink, such as viscosity or flowability, adherence to the writing substrate, etc. There are many ways in which writing instruments, and the inks contained therein, have been altered physically or chemically to reduce the incidence of leakage of the ink from the writing instrument.
As it was theorized that ink leakage could be linked to the relative surface energies of the ink and the interior of the writing instrument with which it is contacted, there has been disclosure in the prior art of the coating of ink-contacting areas or ink reservoirs within a writing instrument with a polymer to minimize leakage and/or to minimize ink interaction with the interior surface.
Occasionally, there can be a pressure difference between the ink reservoir on the inside of the writing instrument and the external ambient atmosphere. Equilibration of the pressure difference can be relieved by ink flowing out of the internal ink reservoir, i.e., ink leakage. In order to prevent or to inhibit ink leakage from the writing instrument under such circumstances, a buffer ink reservoir is disclosed in the prior art into which overflow ink may be stored. The overflow ink can be returned to the internal ink reservoir upon equilibration of the pressure difference.
Superabsorbent polymers and copolymers are well known in the scientific literature for their utility in absorbing water, saline, and a variety of bodily fluids, such as urine (natural or artificial), blood, etc., and particularly for their use in practical applications such as diapers, incontinence pads, feminine hygiene products, and the like. However, the use of absorbent polymers or copolymers in applications involving writing media is scant at best.
Although absorbent polymers and copolymers have been used in absorbing printing inks, the prior art offers no guidance as to the use of superabsorbent polymers or copolymers to absorb other types of inks, such as used in hand-held or finger-manipulable writing instruments.
It would be desirable to design a writing instrument that has reduced leakage of ink within or from its interior. It would be particularly desirable to design and/or to produce a leak resistant writing instrument containing an ink absorbing component located in areas particularly prone to ink leakage.